1. Field of the Invention
This invention relates generally to servoing systems, and more particularly to an improved servoing system for use in positioning read/write heads in magnetic recording or reproducing equipment.
2. Description Of The Prior Art
An important design consideration in magnetic memory systems, especially floppy disk drives, is that the recording medium (diskettes) produced by one manufacturer's equipment may be read by another manufacturer's equipment. In order to meet this requirement clean recording tracks are required. Typical read/write head construction for use in floppy disk drives accordingly utilizes either tunnel or straddle erase techniques to remove fringe flux patterns produced by the write head during a write operation in order to provide clean tracks to accomplish the purpose of record compatibility. The tunnel or straddle erase heads are generally a single coil wrapped on a yoke that spans the read/write core. This technique produces tracks of information that are typically 0.012 inches wide with 0.0088 inch gaps of erased area between the tracks.
In view of the extremely fine spacing between the tracks perfect alignment of the read head is normally somewhat difficult to maintain. Misalignments may be caused, for example, by mechanical tolerances, temperature changes, hygroscopic expansion of the recording medium and other phenomena. Thus a need exist for an improved read head servoing system which can follow a track of recorded information with extreme accuracy, particularly in the environment of a floppy disk drive.
Systems of this type have been disclosed in the past, for example in U.S. Pat. No. 3,246,307, issued Apr. 12, 1966 to C. B. Stanley which describes a servo positioning system for use with a magnetic disk file. The device disclosed in this patent includes a unique read/write head structure comprised of three separate elements, one writing element and two separate reading heads, each about 1/3 the width of the recorded track. A second disclosed embodiment in the patent utilizes a read/write head having two separated magnetic elements. While the system described in the Stanley patent is functional in some environments, it is not satisfactory for accurate fine positioning of a read/write head in a floppy disk drive system. In particular, the fine position servo of the Stanley patent is used only for initial fine positioning of the read/write head. Once positioning is completed, the servo is disconnected for the remainder of the read operation. Due to the nature of the floppy disk medium however, it is important that fine position servoing be continued throughout any read operation. Furthermore, the compatibility requirement, previously mentioned, could not be obtained by the Stanley apparatus because it contains no tunnel or straddle erase heads to erase fringe flux reversals at the sides of the recorded track. In addition, the use of multiple, relatively narrow read head elements in the Stanley device reduces the signal-to-noise ratios obtainable by the disclosed system.
From the foregoing, it is believed apparent that an improved system for track servoing, particularly in conjunction with disk drives, is needed.